This invention relates to a cutting device for reducing waste material, comprising at least two groups of knives mounted on a shaft, next to one another, installed rotatably in front of an anvil, the said groups of knives comprising each several splitting knives, intended to split the waste material mainly according to the sense of supply and comprising at least one chopping knife, intended to cut the waste material mainly across the sense of supply of the waste material to be cut.
The invention relates, for instance, to a cutting device to uniformly reduce waste material, more particularly a cutting device for shredding all sorts of organic material (garden waste, loppings, branches, leaves, agricultural crops, foliage, . . . ).
The invention more particularly relates to a cutting device, in which a number of groups of knives, composed of fixed splitting knives and chopping knives, are mounted on a shaft next to one another and are rotating in a housing where they cut the waste material by interacting with an anvil and a calibrating sieve.
The organic waste material, more particularly wood, (this being the hardest form of green waste material), is composed of fibres running lengthwise within their structure. If it is required to cut across a bundle of fibres, more particularly a branch, all the fibres should be cut across, an operation which requires quite some energy, and the thicker the wood, the more fibres have to be cut across.
Now, various systems are known, hitting across the loppings by means of a chopping knife or a drawknife on a counterknife, in order to shred the waste material.
A first known system is the disc chipper, where a number of knives are mounted in the plane of the large disc against which the wood is pushed and chopped off between the knives and a counterknife.
A second known system is the shave chipper, in which a number of knives are mounted lengthwise along the wall of a drum. The wood is pushed against the wall of the drum, causing the wood to be chopped crosswise between the knives and a counterknife.
Irrespective of their construction, both systems have a number of serious drawbacks:                both systems require rather much energy;        ligneous material is transformed into compressed shreds, difficult to compost;        green material or material rich in leaves is hardly or not at all reduced;        the cutting parts are sensitive to wear;        
Another, very frequently found system is chopping wood in the sense of the fibre by means of flails or hammers. This is a system in which the rotor is composed of a number of discs on which, or between which, loose cutting elements have been suspended. These freely suspended flails or hammers will smash the green waste material to pieces.
Similar systems likewise require a lot of power, because they crush the material mainly by the striking power of the cutting elements. Additionally, these systems produce shreds of a very irregular shape and size as garden waste may pass between the striking hammers, because they are not mounted against one another.
Also in EP 0 785 026 a cutting device is described for reducing waste material. More particularly, this is a cutting device comprising an anvil and groups of knives mounted on a shaft having fixed knives. Within a group of knives, the extremities of the knives have been installed in a manner shifted with respect to one another, so that the projections of the cutting faces on the anvil overlap each other or run into one another.
Although it is possible to shred the waste material over the total width of supply by means of such a device, and the position of the knives allows for a better cutting efficiency, the cutting device described in EP 0 785 026 it is not always able to cut the waste material in an optimal manner (especially in case of a tough and fibrous green waste material).
WO-01/64018 is essentially based on EP 0 785 026 and tries to find a solution to the above-mentioned drawback by adding cross knives to the cutting device described in EP 0 785 026. However, each cross knife is chopping over the entire width of supply all in one go, because of which this construction brings along a few serious drawbacks:                a higher power consumption, because the material supplied to each cross knife causes the rotor to slow down at the same moment;        a higher and pulsating noise level;        a higher sensitivity to damage (in case a strange object is introduced) because there is less chance to avoid the cross knife which has the same width as the machine;        heavy vibrations on the wood (kick-back effect);        the material (for instance, branches) is pulled in aggressively, causing danger to the operators.        
An additional drawback of the system mentioned above, but also of the disc and shave shredder, is that the size of the shreds is mainly determined by the cutting frequency of the cross knife and the rate and speed of supply. As these two factors are determined by the construction of the machine, it is difficult to determine an invariable size of chips or shreds at changing material to be shredded (different kinds of green waste material). At the same time, the wood is projected into the discharge channel as soon as it is chopped off, so that it leaves the shredding system immediately and no additional shredding will occur in the shredding chamber.
The purpose of this invention is to propose a cutting device not showing the drawbacks mentioned above, which will shred any material uniformly and finely at the lowest possible energy consumption.